Motor drive device and brushless motor

Abstract

Provided is a motor drive device which performs switching, with respect to a synchronous motor including a stator around which a motor winding is wound and a rotor holding a permanent magnet, from a synchronous operation in which the synchronous motor is synchronously driven to position-sensorless vector control in which a current supplied to the motor winding is controlled based on a position of the rotor. During the synchronous operation, the present motor drive device calculates, by estimation, an induced voltage error based on the detected current and voltage, performs control of an amplitude of a current instruction such that an error, of a target induced voltage, calculated based on an estimated induced voltage and based on an internal angle becomes equal to the induced voltage error, and switches the mode to the sensorless mode after the error is reduced to be within a range of a predetermined value. Further, by gradually reducing the current instruction during the synchronous operation, the absolute value of the induced voltage error is reduced to be within a range of the predetermined value.

The invention claimed is: 
     
       1. A motor drive device which performs switching, with respect to a synchronous motor including a stator around which a motor winding is wound and a rotor holding a permanent magnet, from a synchronous operation in which the synchronous motor is synchronously driven to position-sensorless vector control in which current supplied to the motor winding is controlled based on a position of the rotor,
 wherein, 
 current having a predetermined amplitude is started to be supplied to the motor winding when the synchronous motor is stopped, 
 frequency of the current is gradually increased, so that motor speed is accelerated to a predetermined synchronous speed, and 
 the frequency of the current is maintained constant so that the predetermined synchronous speed is maintained, and 
 wherein the motor drive device calculates an induced voltage error based on a detected current and voltage, reduces an absolute value of the induced voltage error to within a predetermined value, and then switches from the synchronous operation to the position-sensorless vector control. 
 
     
     
       2. The motor drive device according to  claim 1 , wherein the absolute value of the induced voltage error is reduced to within a predetermined value by gradually reducing a current instruction of the current flowing in the motor winding during the predetermined synchronous speed operation. 
     
     
       3. A brushless motor comprising the motor drive device according to  claim 1 .